Sunscreen is a common term for skin care products that absorb UV radiation and dissipate it as heat.
Ultraviolet radiation arrives at the skin most often in three distinct wavelengths, designated UV-A, -B, and -C. UV-A has the longest wavelength at 400 nm-320 nm and therefore penetrates deeper into skin than the others, causing age spots and wrinkling, UV-B, with a wavelength of 320 nm-290 nm, is the primary cause of sunburns and the targeted range for protection, though Broad-spectrum sunscreens will inhibit both UV-A and UV-B. UV-C has a wavelength of 290 nm-100 nm, though it is completely blocked by the ozone layer.
Sunscreen is applied. After a period of time, the sunscreen wears off and its effectiveness diminishes, until the skin has lost all protection. The amount of time for this to occur depends on several factors: exposure to sun, amount of sunscreen applied initially, moisture in the air or skin, and the wearer's amount of physical activity.
The ability to detect if sufficient sunscreen has been applied to a particular skin area, and the ability to detect if the sunscreen is providing adequate protection, are two of the biggest challenges when using sunscreen. Neither sunscreen nor UV light are visible to the eye, making it difficult for consumers to tell if they have applied sufficient sunscreen, and whether it is providing adequate protection over the duration of sun exposure.
There thus remains a need for a low cost, easy to use device that tells a user whether they have applied enough sunscreen to their skin.